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Abstract:

A polishing method can obtain a good polishing profile which, for
example, will not cause peeling of a semiconductor layer from a silicon
substrate. The polishing method includes: positioning a polishing head at
a position above a polishing start position in an edge portion of a
rotating substrate; lowering a polishing tool of the polishing head until
the polishing tool comes into contact with the polishing start position
in the edge portion of the rotating substrate and a pressure between the
polishing tool and the polishing start position reaches a set pressure;
allowing the polishing tool to stay at the polishing start position for a
predetermined amount of time; and then moving the polishing head toward a
peripheral end of the substrate while keeping the polishing tool in
contact with the edge portion of the rotating substrate at the set
pressure.

Claims:

1. A polishing method comprising: positioning a polishing head at a
position above a polishing start position in an edge portion of a
rotating substrate; lowering the polishing head and bringing a polishing
tool of the polishing head into contact with the polishing start position
in the edge portion of the rotating substrate at a predetermined
pressure; allowing the polishing tool to stay at the polishing start
position for a predetermined amount of time; and then moving the
polishing head toward a peripheral end of the substrate while keeping the
polishing tool in contact with the edge portion of the rotating substrate
at the predetermined pressure.

2. The polishing method according to claim 1, herein the predetermined
amount of time is at least one second.

3. The polishing method according to claim 1, wherein the polishing tool
is a polishing tape which travels in one direction at a predetermined
speed when it polishes the edge portion of the substrate.

4. The polishing method according to claim 1, wherein a bevel portion of
the substrate is polished while polishing the edge portion of the
substrate by keeping the polishing tool in contact with the edge portion
of the rotating substrate.

5. A polishing method comprising: positioning a polishing head at a
position above a polishing start position in an edge portion of a
rotating substrate; lowering a polishing tool of the polishing head until
the polishing tool comes into contact with the polishing start position
in the edge portion of the rotating substrate and a pressure between the
polishing tool and the polishing start position reaches a set pressure;
allowing the polishing tool to stay at the polishing start position for a
predetermined amount of time; and then moving the polishing head toward a
peripheral end of the substrate while keeping the polishing tool in
contact with the edge portion of the rotating substrate at the set
pressure.

6. The polishing method according to claim 5, wherein the predetermined
amount of time is at least one second.

7. The polishing method according to claim 5, wherein during a period
after contact of the polishing tool with the edge portion of the
substrate until the start of movement of the polishing head, the contact
pressure of the polishing tool on the edge portion of the substrate is
kept higher than the set pressure.

8. The polishing method according to claim 5, wherein after lowering the
polishing tool and bringing the polishing tool into contact with the
polishing start position in the edge portion of the rotating substrate at
a lower pressure than the set pressure, the pressure of the polishing
tool on the edge portion of the substrate is increased to the set
pressure.

9. The polishing method according to claim 5, wherein the polishing tool
is a polishing tape which travels in one direction at a predetermined
speed when it polishes the edge portion of the substrate.

10. The polishing method according to claim 5, wherein a bevel portion of
the substrate is polished while polishing the edge portion of the
substrate by keeping the polishing tool in contact with the edge portion
of the rotating substrate.

11. A polishing method comprising: a first polishing including (a)
positioning a polishing head at a position above a polishing start
position in an edge portion of a rotating substrate, (b) lowering a
polishing tool of the polishing head until the polishing tool comes into
contact with the polishing start position in the edge portion of the
rotating substrate and a pressure between the polishing tool and the
polishing start position reaches a set pressure, and (c) moving the
polishing head toward a peripheral end of the substrate at a first
movement speed while keeping the polishing tool in contact with the edge
portion of the rotating substrate; and a second polishing including (d)
moving the polishing head toward the peripheral end of the substrate at a
second movement speed while keeping the polishing tool in contact with
the edge portion of the rotating substrate.

12. The polishing method according to claim 11, wherein the second
movement speed of the polishing head is higher than the first movement
speed of the polishing head.

13. The polishing method according to claim 11, wherein when moving the
polishing head toward the peripheral end of the substrate at the first
movement speed, the contact pressure of the polishing tool on the edge
portion of the substrate is kept higher than the set pressure.

14. The polishing method according to claim 11, wherein after lowering
the polishing tool and bringing the polishing tool into contact with the
polishing start position in the edge portion of the rotating substrate at
a lower pressure than the set pressure, the pressure of the polishing
tool on the edge portion of the substrate is increased to the set
pressure.

15. The polishing method according to claim 11, wherein the polishing
tool is a polishing tape which travels in one direction at a
predetermined speed when it polishes the edge portion of the substrate.

16. The polishing method according to claim 11, wherein a bevel portion
of the substrate is polished while polishing the edge portion of the
substrate by keeping the polishing tool in contact with the edge portion
of the rotating substrate.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a polishing method for polishing a
peripheral portion (edge portion and bevel portion) of a substrate, such
as a semiconductor wafer, and more particularly to a polishing method for
polishing or grinding a peripheral portion of a semiconductor wafer in
the process of manufacturing a semiconductor device in a surface of the
semiconductor wafer.

[0003] 2. Description of the Related Art

[0004] A polishing apparatus, which uses a polishing tape having abrasive
particles fixed on a surface, is known as a polishing apparatus for
polishing a peripheral portion (edge portion and bevel portion) of a
substrate, such as a semiconductor wafer (see Japanese Patent No.
4125148). In polishing of a peripheral portion (edge portion and bevel
portion) of a semiconductor wafer by the use of a polishing tape, it is
common practice to press a surface of the polishing tape against the
peripheral portion of the semiconductor wafer, rotating in a horizontal
plane, at a set pressure while supplying a polishing liquid, such as pure
water, to a surface of the semiconductor wafer.

[0005] In a semiconductor wafer W shown in FIG. 1, for example, the "bevel
portion" herein refers to a portion B consisting of an upper inclined
portion P and a lower inclined portion Q of an upper surface and a lower
surface, respectively, of the semiconductor wafer W, and a peripheral
side surface portion R of the semiconductor wafer W. The "edge portion"
of the semiconductor wafer W shown in FIG. 1, for example, herein refers
to a portion E lying between the boundary of the bevel portion B and a
device area D of the upper surface in which semiconductor devices are
formed.

[0006] A commonly-known polishing apparatus for polishing an edge portion
of a substrate with a polishing tape includes a horizontally movable
polishing head in which a polishing tape is held movably in one
direction. In operation of this polishing apparatus, the polishing head
is positioned immediately above a polishing start position in an edge
portion of a rotating substrate, and the polishing tape is lowered and
brought into contact with the polishing start position in the edge
portion of the rotating substrate. When the contact pressure (load) of
the polishing tape on the edge portion of the substrate is found to have
reached a set pressure, the polishing tape is allowed to move (scan)
toward the peripheral end of the substrate at a predetermined movement
speed while keeping the polishing tape in contact with the edge portion
of the rotating substrate.

[0007] The applicant has proposed a polishing apparatus which can polish a
peripheral portion (edge portion) of a substrate, including a flat
portion, with a polishing tape while maintaining the original angle of
the peripheral portion (see Japanese Patent Laid-Open Publication No.
2009-208214). The applicant has also proposed a polishing apparatus which
is suited for polishing of a bevel portion of a substrate, can shorten
the overall polishing time and can facilitate replacement of polishing
tape (see Japanese Patent Laid-Open Publication No. 2009-154285).

[0008] It has recently been proposed to manufacture a bonded substrate,
such as an SOI (silicon-on-insulator) substrate, by a bonding method
which involves bonding, through heat treatment or the like, two silicon
substrates (a device substrate having semiconductor devices and a
supporting substrate). In a known method for manufacturing a bonded
substrate, such as an SOI substrate, a first silicon substrate (device
substrate), having a surface semiconductor layer (SOI layer) and whose
surface edge portion has been polished away as necessary, and a second
silicon substrate (supporting substrate), facing each other, are bonded
via an insulting film, and then the back surface of the first silicon
substrate (device substrate) is polished or etched away, leaving the
semiconductor layer. Thereafter, an entire peripheral portion of the
semiconductor layer is polished away, and an edge portion of the second
silicon substrate is polished to a predetermined depth (see Japanese
Patent Laid-Open Publication No. H4-85827).

SUMMARY OF THE INVENTION

[0009] With reference to the conventional polishing apparatus which
includes a polishing head and in which a polishing tape is lowered and
brought into contact with a polishing start position in an edge portion
of a rotating substrate and, when the contact pressure of the polishing
tape on the edge portion of the substrate is found to have reached a set
pressure, the polishing tape is allowed to move toward the peripheral end
of the substrate at a predetermined movement speed while keeping the
polishing tape in contact with the edge portion of the rotating
substrate, it is generally difficult to bring the polishing tape into
contact with the polishing start position in the edge portion of the
substrate at a set pressure upon the start of polishing and, in addition,
the polishing tape stays in the polishing start position generally for
only a short time. The conventional polishing apparatus, therefore, has
the problem that a polished surface of a substrate, at the boundary with
the non-polished surface, is likely to suffer from insufficient polishing
or uneven polishing.

[0010] Especially when manufacturing a bonded wafer, such as an SOI
substrate, by the above-described method in which a first silicon
substrate (device substrate), having a surface semiconductor layer, and a
second silicon substrate (supporting substrate), facing each other, are
bonded via an insulting film, and then the back surface of the first
silicon substrate (device substrate) is polished or etched away, leaving
the semiconductor layer, and thereafter the entire peripheral portion of
the semiconductor layer is polished away, and the edge portion of the
second silicon substrate is polished to a predetermined depth, the
semiconductor layer is likely to peel off the second silicon substrate
(supporting substrate) if insufficient polishing or uneven polishing
occurs at the boundary of the polished surface with the non-polished
surface.

[0011] The present invention has been made in view of the above situation.
It is therefore an object of the present invention to provide a polishing
method which, e.g., when manufacturing a bonded wafer, such as an SOI
substrate, by the above-described method comprising polishing away an
entire peripheral portion of a semiconductor layer of a first silicon
substrate, and polishing an edge portion of a second silicon substrate to
a predetermined depth, can obtain a good polishing profile which will not
cause peeling of the semiconductor layer from the second silicon
substrate.

[0012] In order to achieve the above object, the present invention
provides a polishing method comprising: positioning a polishing head at a
position above a polishing start position in an edge portion of a
rotating substrate; lowering the polishing head and bringing a polishing
tool of the polishing head into contact with the polishing start position
in the edge portion of the rotating substrate at a predetermined
pressure; allowing the polishing tool to stay at the polishing start
position for a predetermined amount of time; and then moving the
polishing head toward a peripheral end of the substrate while keeping the
polishing tool in contact with the edge portion of the rotating substrate
at the predetermined pressure.

[0013] According to this polishing method, while keeping the polishing
tool in contact with a polishing start position in an edge portion of a
rotating substrate at a predetermined pressure, the polishing tool is
allowed to stay at the polishing start position for a predetermined
amount of time to polish the edge portion at the polishing start
position. This can prevent the occurrence of insufficient polishing or
uneven polishing at the boundary of the polished surface with the
non-polished surface, making it possible to obtain a good polishing
profile which, e.g., will not cause peeling of a surface film, such as a
semiconductor layer, from the substrate. Furthermore, even when a film to
be polished away is present in an edge portion of a substrate in an
uneven distribution in the circumferential direction, the film to be
polished away can be securely prevented from remaining in the edge
portion of the substrate by setting the polishing tool stay time based on
the location hardest to polish.

[0014] The present invention also provides a polishing method comprising:
positioning a polishing head at a position above a polishing start
position in an edge portion of a rotating substrate; lowering a polishing
tool of the polishing head until the polishing tool comes into contact
with the polishing start position in the edge portion of the rotating
substrate and a pressure between the polishing tool and the polishing
start position reaches a set pressure; allowing the polishing tool to
stay at the polishing start position for a predetermined amount of time;
and then moving the polishing head toward a peripheral end of the
substrate while keeping the polishing tool in contact with the edge
portion of the rotating substrate at the set pressure.

[0015] According to this polishing method, while keeping the polishing
tool in contact with a polishing start position in an edge portion of a
rotating substrate at a set pressure, the polishing tool is allowed to
stay at the polishing start position for a predetermined amount of time
to polish the edge portion at the polishing start position. This can
prevent the occurrence of insufficient polishing or uneven polishing at
the boundary of the polished surface with the non-polished surface,
making it possible to obtain a good polishing profile which, e.g., will
not cause peeling of a surface film, such as a semiconductor layer, from
the substrate.

[0016] In a preferred aspect of the present invention, the predetermined
amount of time is preferably at least one second.

[0017] In a preferred aspect of the present invention, during a period
after contact of the polishing tool with the edge portion of the
substrate until the start of movement of the polishing head, the contact
pressure of the polishing tool on the edge portion of the substrate is
kept higher than the set pressure.

[0018] Thus, the polishing rate can be increased when an edge portion of a
substrate is polished while allowing the polishing tool to stay at the
polishing start position in the edge portion of the substrate for a
predetermined amount of time. This can prevent lowering of the
throughput. In view of stress exerting on the substrate, it is also
possible to raise the rotational speed of the substrate.

[0019] The present invention also provides a polishing method comprising:
a first polishing step including (a) positioning a polishing head at a
position above a polishing start position in an edge portion of a
rotating substrate, (b) lowering a polishing tool of the polishing head
until the polishing tool comes into contact with the polishing start
position in the edge portion of the rotating substrate and a pressure
between the polishing tool and the polishing start position reaches a set
pressure, and (c) moving the polishing head toward a peripheral end of
the substrate at a first movement speed while keeping the polishing tool
in contact with the edge portion of the rotating substrate; and a second
polishing including (d) moving the polishing head toward the peripheral
end of the substrate at a second movement speed while keeping the
polishing tool in contact with the edge portion of the rotating
substrate.

[0020] By thus carrying out polishing of an edge portion of a substrate in
two steps at different polishing rates, a film to be polished away,
existing in the edge portion of the substrate, can be polished under
polishing conditions appropriate for the particular film. Further, the
inclination of a stepped portion, formed at the boundary between the
polished surface and the non-polished surface of the substrate, can be
arbitrarily changed by changing polishing conditions.

[0021] The second movement speed of the polishing head is preferably
higher than the first movement speed of the polishing head.

[0022] This can prevent the occurrence of insufficient polishing or uneven
polishing at the boundary of the polished surface of a substrate with the
non-polished surface, making it possible to obtain a good polishing
profile.

[0023] In a preferred aspect of the present invention, when moving the
polishing head toward the peripheral end of the substrate at the first
movement speed, the contact pressure of the polishing tool on the edge
portion of the substrate is kept higher than the set pressure.

[0024] Thus, the polishing rate can be increased when the polishing head
is moving toward the peripheral end of the substrate at the first
movement speed. This can prevent lowering of the throughput. In view of
stress exerting on the substrate, it is also possible to raise the
rotational speed of the substrate.

[0025] In a preferred aspect of the present invention, after lowering the
polishing tool and bringing the polishing tool into contact with the
polishing start position in the edge portion of the rotating substrate at
a lower pressure than the set pressure, the pressure of the polishing
tool on the edge portion of the substrate is increased to the set
pressure.

[0026] This can minimize the stress exerting on the substrate when the
descending polishing tool comes into contact with the polishing start
position in the edge portion of the rotating substrate. In the absence of
a hard member, such as a stage, which supports an edge portion of a
substrate from below, a stress exerting on the substrate could bend the
substrate, which can result in the formation of a crack in the substrate
and, in the worst case, breakage of the substrate. Such problems can be
prevented by minimizing the stress exerting on the substrate in the
above-described manner.

[0027] The polishing tool may preferably be a polishing tape which travels
in one direction at a predetermined speed when it polishes the edge
portion of the substrate.

[0028] In a preferred aspect of the present invention, a bevel portion of
the substrate is polished while polishing the edge portion of the
substrate by keeping the polishing tool in contact with the edge portion
of the rotating substrate.

[0029] The throughput can be increased by thus simultaneously polishing
the edge portion and the bevel portion of the substrate while rotating
the substrate.

[0030] A polishing apparatus may comprises: a substrate holding section
for holding and rotating a substrate in a horizontal position; a
horizontally movable polishing head including a vertically movable
polishing tool for polishing an edge portion of the substrate by pressing
it against the edge portion of the rotating substrate held in a
horizontal position by the substrate holding section; and a control
section for controlling the movement of the polishing head, wherein the
control section controls the polishing head in such a manner that after
the polishing tool has come into contact with a polishing start position
in the edge portion of the rotating substrate and the contact pressure
has reached a set pressure, the polishing tool is allowed to stay at the
polishing start position for a predetermined amount of time, and
thereafter the polishing head moves toward the peripheral end of the
substrate while keeping the polishing tool in contact with the edge
portion of the rotating substrate at the set pressure.

[0031] Alternatively, a polishing apparatus may comprises: a substrate
holding section for holding and rotating a substrate in a horizontal
position; a horizontally movable polishing head including a vertically
movable polishing tool for polishing an edge portion of the substrate by
pressing it against the edge portion of the rotating substrate held in a
horizontal position by the substrate holding section; and a control
section for controlling the movement of the polishing head, wherein the
control section controls the polishing head in such a manner that after
the polishing tool has come into contact with a polishing start position
in the edge portion of the rotating substrate and the contact pressure
has reached a set pressure, the polishing head moves toward the
peripheral end of the substrate at a first movement speed while keeping
the polishing tool in contact with the edge portion of the rotating
substrate, and thereafter the polishing head moves toward the peripheral
end of the substrate at a second movement speed while keeping the
polishing tool in contact with the edge portion of the rotating
substrate.

[0032] The polishing apparatuses may further comprise a bevel polishing
head for polishing a bevel portion of the rotating substrate.

[0033] The present invention makes it possible to prevent the occurrence
of insufficient polishing or uneven polishing at the boundary of a
polished surface of a substrate with a non-polished surface, and to
obtain a good polishing profile which, e.g., will not cause peeling of a
surface film, such as a semiconductor layer, from the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 is a cross-sectional view illustrating a bevel portion and
an edge portion of a semiconductor wafer;

[0036] FIG. 3 is a side view showing a tilt mechanism for tilting a
polishing head of the polishing apparatus shown in FIG. 2;

[0037] FIGS. 4A through 4D are diagrams illustrating, in a sequence of
process steps, the relationship between the polishing head and a
substrate upon polishing of an edge portion of the substrate in the
polishing apparatus shown in FIG. 2;

[0038] FIG. 5 is a graph showing an exemplary relationship between the
movement speed of the polishing head and time upon polishing of an edge
portion of a substrate in the polishing apparatus shown in FIG. 2;

[0039] FIGS. 6A though 6C are graphs showing other exemplary relationships
between the movement speed of the polishing head and time upon polishing
of an edge portion of a substrate in the polishing apparatus shown in
FIG. 2;

[0040] FIG. 7 is a graph showing the relationship between polishing amount
and radial position on a substrate in Example 1;

[0041] FIG. 8 is a graph showing the relationship between polishing amount
and radial position on a substrate in Example 2;

[0042] FIG. 9 is a graph showing the relationship between polishing amount
and radial position on a substrate in Comp. Example 1

[0043] FIG. 10 is a photomicrograph of a substrate surface after polishing
(rough polishing) of an edge portion of a substrate, showing a surface
area around the boundary between the polished surface and the
non-polished surface;

[0044] FIG. 11 is a photomicrograph of a substrate surface after polishing
of an edge portion of a substrate in Example 3, showing a surface area
around the boundary between the polished surface and the non-polished
surface;

[0045] FIG. 12 is a photomicrograph of a substrate surface after polishing
of an edge portion of a substrate in Example 4, showing a surface area
around the boundary between the polished surface and the non-polished
surface;

[0046] FIG. 13 is a photomicrograph of a substrate surface after polishing
of an edge portion of a substrate in Comp. Example 2, showing a surface
area around the boundary between the polished surface and the
non-polished surface; and

[0047] FIG. 14 is a schematic view of another polishing apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] Preferred embodiments of the present invention will now be
described in detail with reference to the drawings. FIG. 2 is a schematic
front view showing a polishing apparatus. As shown in FIG. 2, this
polishing apparatus includes a substrate holding section 1 for holding
and rotating a substrate W, such as a semiconductor wafer, in a
horizontal position, a polishing head 2 for polishing an edge portion of
the substrate W held by the substrate holding section 1, and a support
section 3 for supporting, from the back surface of the substrate W, the
edge portion of the substrate W held by the substrate holding section 1.

[0049] The substrate holding section 1 includes a substrate stage 11 for
holding the substrate W, e.g., by vacuum attraction, and a substrate
rotating mechanism 12 for rotating the substrate stage 11. The substrate
stage 11 has a smaller diameter than the substrate W so that the
substrate W is held with the edge portion lying outside the substrate
stage 11. The substrate rotating mechanism 12 has a not-shown motor which
is coupled to the substrate stage 11. Thus, the substrate W held on the
substrate stage 11 rotates in a horizontal plane by rotating the motor of
the substrate rotating mechanism 12.

[0050] The polishing head 2 is provided with a polishing tape 10 as a
polishing tool for polishing the edge portion of the substrate W by
pressing it against the edge portion of the surface (upper surface) of
the substrate W. In this embodiment, the polishing tape 10 is used as a
polishing tool. A polishing tape having abrasive particles, such as
diamond particles or SiC particles, fixed on one surface of a base film,
can be used as the polishing tape 10. The surface of the polishing tape
10, on which the abrasive particles are fixed, serves as a polishing
surface. The abrasive particles of the polishing tape 10 may be
appropriately selected depending on the type of the substrate W, the
polishing performance required, etc. For example, diamond particles or
SiC particles, having an average particle size in the range of 0.1 μm
to 5.0 μm, can be used as the abrasive particles. It is also possible
to use a belt-like polishing cloth having no abrasive particles. A film
made of a material having flexibility, such as polyester, polyurethane,
polyethylene terephthalate, etc., can be used as the base film.

[0051] The substrate holding section 1, the polishing head 2 and the
support section 3 are housed in a not-shown housing, and the interior
space of the hosing constitutes a polishing room. The polishing tape 10
is fed to the polishing head 2 from a polishing tape supply mechanism 15
which is disposed outside the polishing room. The polishing tape supply
mechanism 15 is secured to the housing or a not-shown frame, so that the
position of the mechanism 15 is fixed. The polishing tape supply
mechanism 15 includes a tape feeding mechanism 16 and a tape roll-up
mechanism 17. The polishing tape 10 is fed from the tape feeding
mechanism 16 to the polishing head 2, and is recovered from the polishing
head 2 by the tape roll-up mechanism 17. Because the polishing tape 10 is
thus fed continuously and gradually from the polishing tape supply
mechanism 15 to the polishing head 2, polishing of the substrate W is
performed always by a new polishing surface.

[0052] The polishing head 2 includes a pressing pad 20 disposed on the
back side (opposite side from the polishing surface) of the polishing
tape 10, and a pressing mechanism 21, e.g., comprised of a stepping motor
or a servomotor, for applying a pressure to the pressing pad 20. The
position and the rotational speed of the pressing mechanism 21 are
controllable. The pressing pad 20 is secured to a front end of a rod 22
which extends from the pressing mechanism 21 and which is supported by a
not-shown bearing slidably in the longitudinal direction thereof. A
pressure is applied by the pressing mechanism 21 to the pressing pad 20
via the rod 22 so as to press the polishing surface of the polishing tape
10 against the surface of the substrate W. The pressure applied to the
polishing tape 10 is detected, e.g., by a pressure sensor provided
between the front end of the rod 22 and the pressing pad 20 or a torque
sensor which detects the motor torque, and is controlled, e.g., at a set
load (pressure), whereby the stop (stay) position of the polishing tape
10 in the vertical direction is adjusted. Examples of materials usable
for the pressing pad 20 include elastic materials such as silicone
rubber, a silicone sponge, fluororubber, etc., and rigid materials such
as polybutylene naphthalate (PBN), fluororesin, polyether ether ketone
(PEEK), etc.

[0053] Instead of the above-described motor, it is possible to use an air
cylinder as a drive mechanism for the pressing mechanism 21. Also in this
case, it is possible to measure the pressure applied to the polishing
tape 10, e.g., with a pressure sensor provided between the front end of
the rod 22 and the pressing pad 20 or with a pressure gauge which
measures the air pressure in the air cylinder, and to adjust the pressure
on the polishing tape 10 to a set load (pressure) by adjusting the
pressure of air supplied to the air cylinder, thereby accurately
controlling the pressure of the polishing tape 10 during polishing.

[0054] FIG. 3 is a side view showing a tilt mechanism for tilting the
polishing head 2. The polishing head 2 is coupled to a motor 29 via an
arm 26, a belt 27 and pulleys 28A, 28B, so that by the actuation of the
motor 29, the polishing head 2 rotates (tilts) around the peripheral end
of the substrate W on the substrate holding section 1. The arm 26, the
belt 27, the pulleys 28A, 28B and the motor 29 constitute a tilt
mechanism for tilting the polishing head 2.

[0055] The polishing head 2 is supported via the tilt mechanism by a plate
30 which is provided on a sliding mechanism 31. The sliding mechanism 31
allows the plate 30 to move in the longitudinal direction of the sliding
mechanism 31. The plate 30 is coupled to a linear actuator 33 whose stop
position and movement speed are controllable, so that by the actuation of
the linear actuator 33, the polishing head 2 moves in the radial
direction of the substrate W held on the substrate holding section 1.
Thus, the linear actuator 33 constitutes a movement mechanism for moving
the polishing head 2 in the radial direction of the substrate W.

[0056] The polishing head 2 is disposed on the front surface (upper
surface) side of the substrate W held on the substrate holding section 1,
while the support section 3 is disposed on the back surface (lower
surface) side of the substrate W. Thus, the polishing head 2 and the
support section 3 are approximately vertically symmetrical with respect
to the substrate W. The support section 3 supports the edge portion of
the substrate W, which is being pressed on by the polishing head 2, from
the opposite side (back side) of the substrate W from the edge portion by
utilizing the pressure of a fluid, as described below.

[0057] The support section 3 is coupled via a sliding mechanism 34 to the
plate 30 that supports the polishing head 2. The sliding mechanism 34 is
coupled to a not-shown linear actuator mounted to the plate 30. The
support section 3 is thus movable in the radial direction of the
substrate W independently of the polishing head 2. The support section 3
is connected to a liquid supply source 36 via a pressure-reducing valve
35. A liquid, whose pressure is adjusted by the pressure-reducing valve
35, is supplied to the support section 3. The support section 3 has a
nozzle 37 located near a back surface portion opposite to the edge
portion of the substrate W. The liquid whose pressure has been adjusted
by the pressure-reducing valve 35 is ejected from the nozzle 37 toward
the edge portion of the back surface of the substrate W. Pure water is
preferably used as the liquid.

[0058] A polishing liquid supply nozzle 40 for supplying a polishing
liquid, such as pure water, onto the front surface (upper surface) of the
substrate W is disposed at a position above the central portion of the
substrate W held on the substrate holding section 1. The polishing
apparatus also includes a control section 42 for controlling the
not-shown motor of the substrate rotating mechanism 12, the pressing
mechanism 21 of the polishing head 2, and the linear actuator 33 which
constitutes the movement mechanism for moving the polishing head 2 in the
radial direction of the substrate W.

[0059] The control section 42 controls the rotational speed of the
not-shown motor of the substrate rotating mechanism 12, the pressing load
and the stop position of the pressing mechanism 21 of the polishing head
2, the stop position and the movement speed of the linear actuator 33,
etc.

[0060] Polishing of an edge portion of a substrate by the polishing
apparatus of this embodiment will now be described with reference further
to FIGS. 4 and 5.

[0061] A substrate W is transported by a not-shown transport robot into
the polishing room of the polishing apparatus and placed on the substrate
stage 11 of the substrate holding section 1. The substrate holding
section 1, while performing centering of the substrate W, holds the
substrate W, e.g., by vacuum attraction and rotates it in a horizontal
plane. At the same time, a polishing liquid, such as pure water, begins
to be supplied from the polishing liquid supply nozzle 40 onto the
surface (upper surface) of the substrate W.

[0062] Next, the polishing head 2, located in a stand-by position beside
the substrate W held on the substrate holding section 1, as shown in FIG.
4A, is moved by the actuation of the linear actuator 33 to a position
immediately above a polishing start position, where the distance L1
from the peripheral end of the substrate W to the pressing pad 20 is,
e.g., 1.3 mm, in the edge portion of the substrate W, as shown in FIG.
4B. By the actuation of the linear actuator 33, the support section 3
moves to a position immediately below the polishing start position in the
edge portion of the substrate W.

[0063] After the rotational speed of the substrate W is found to have
reached a predetermined rotational speed, the polishing tape supply
mechanism 15 is actuated to allow the polishing tape 10 to travel from
the tape feeding mechanism 16 to the tape roll-up mechanism 17 via the
polishing head 2 and to be rolled up by the tape roll-up mechanism 17. At
the same time, the pressing mechanism 21 is actuated to lower the
pressing pad 20 and gradually bring the polishing tape 10 into contact
with the substrate W, as shown in FIG. 4c, while a liquid is ejected from
the nozzle 37 of the support section 3 toward the edge portion of the
lower surface of the substrate W. Polishing of the edge portion of the
substrate W at a set pressure starts when the polishing tape 10 comes
into contact with the edge portion of the substrate W and the contact
pressure (load) reaches the set pressure.

[0064] Though the pressing pad 20 may be moved at a somewhat high speed,
the pressing mechanism 21 is preferably controlled so that the load
applied from the pressing pad 20 to the substrate W increases gradually.
This can minimize the stress exerting on the substrate W when the
descending polishing tape 10 comes into contact with the polishing start
position in the edge portion of the rotating substrate W. In the absence
of a hard member, such as a stage, which supports an edge portion of a
substrate from below, a stress applied to a substrate could bend the
substrate, which can result in the formation of a crack in the substrate
and, in the worst case, breakage of the substrate. Such problems can be
prevented by minimizing the stress exerting on the substrate W in the
above-described manner.

[0065] As shown in FIG. 5, polishing is continued while keeping the
vertical position of the polishing tape 10 fixed and allowing the
polishing head 2 to stay at the position immediately above the polishing
start position in the edge portion of the substrate W for a predetermined
amount of time between time t1 and time t2 (t2-t1),
t1 being the time when the polishing starts at the set pressure
after the polishing tape 10 has come into contact with the edge portion
of the substrate W and the contact pressure has reached the set pressure.
The predetermined amount of time (t2-t1) is set based on the
location hardest to polish, and is generally at least about one second,
preferably at least 10 seconds, more preferably 20 to 40 seconds.

[0066] Thus, while keeping the polishing tape 10 in contact with the
polishing start position in the edge portion of the rotating substrate W
at the set pressure, the polishing tape 10 is allowed to stay at the
polishing start position for a predetermined amount of time to polish the
edge portion at the polishing start position. This can prevent the
occurrence of insufficient polishing or uneven polishing at the boundary
of the polished surface with the non-polished surface, making it possible
to obtain a good polishing profile which, e.g., will not cause peeling of
a surface film, such as a semiconductor layer, from the substrate W.
Furthermore, even when a film to be polished away is present in the edge
portion of the substrate W in an uneven distribution in the
circumferential direction, the film to be polished away can be securely
prevented from remaining in the edge portion of the substrate W by
setting the stay time of the polishing tape 10 based on the location
hardest to polish.

[0067] The polishing tape 10 may be allowed to stay at the polishing start
position in the edge portion of the substrate W for a predetermined
amount of time while keeping the polishing tape 10 in contact with the
polishing start position at a pressure higher than the set pressure.
According to this manner, the polishing rate can be increased when the
edge portion of the substrate W is polished while allowing the polishing
tape 10 to stay at the polishing start position in the edge portion of
the substrate W for a predetermined amount of time. This can prevent
lowering of the throughput. In view of stress exerting on the substrate,
it is also possible to raise the rotational speed of the substrate W.

[0068] As shown in FIG. 5, after the predetermined amount of time has
elapsed (after time t2), the polishing head 2 is moved at a
predetermined speed V0 toward the peripheral end of the substrate W
while keeping the polishing tape 10 in contact with the edge portion of
the rotating substrate W at the set pressure to continue polishing of the
edge portion of the substrate W with the polishing tape 10. During the
polishing, the angle of the polishing head 2 with respect to the
substrate W may be changed by the tilt mechanism, as necessary.

[0069] After the polishing head 2 has reached a polishing end position
where the distance L2 between the peripheral end of the substrate W
and the pressing pad 20 is, for example, 0.4 mm, the polishing head 2 is
moved at a high speed to the stand-by position beside the substrate W, as
shown in FIG. 4D.

[0070] As shown in FIG. 6A, polishing of the edge portion of the substrate
W may be carried out by a method comprising: carrying out a first
polishing step of moving the polishing head 2 at a first movement speed
V1, e.g., not more than 50 μm/sec, toward the peripheral end of
the substrate W from time t1 when the polishing tape 10 has come
into contact with the edge portion of the substrate W and the contact
pressure reaches the set pressure, while keeping the polishing tape 10 in
contact with the edge portion of the rotating substrate W; carrying out
polishing for a certain distance (up to time t3); and carrying out a
second polishing step of further moving the polishing head 2 at a second
movement speed V2, e.g., 50 μm/sec to 100 μm/sec, toward the
peripheral end of the substrate W while keeping the polishing tape 10 in
contact with the edge portion of the rotating substrate W.

[0071] This polishing method can significantly shorten the polishing time
while preventing the occurrence of insufficient polishing or uneven
polishing at the boundary of the polished surface with the non-polished
surface. In addition, the polishing amount can be made smaller in the
surface area lying closer to a peripheral end of a substrate. This
polishing method is thus especially effective for a substrate in which a
film to be polished away is thinner on the peripheral end side.

[0072] The contact pressure of the polishing tape 10 on the edge portion
of the substrate W during the movement of the polishing head 2 at the
second movement speed V2 may be changed from that during the
movement of the polishing head 2 at the first movement speed V1.
This can further shorten the polishing time.

[0073] In this case, the first movement speed of the polishing head 2 may
be increased linearly from the movement speed V1 to the movement
speed V2, as shown in FIG. 6B, or may be increased gradually from
the movement speed V1 to the movement speed V2, as shown in
FIG. 6c so as to avoid a rapid change in the movement speed of the
polishing head 2.

[0074] The accuracy of positioning of the polishing head 2 is very
important in the above-described embodiment. Because the movement speed
of the polishing head 2 is as low as about 1 μm per second, it is also
very important to enhance the accuracy of the movement speed (amount of
change, error) of the polishing head 2. It is, therefore, preferred to
perform positioning of the polishing head 2 with high accuracy and
accurately control the movement speed of the polishing head 2 by using,
for example, a servomotor or a stepping motor as the linear actuator 33.

[0075] Further, it is preferred that setting values for time to stop the
polishing head 2, the movement speed of the polishing head 2, etc. can be
easily changed through program control by digitalizing and inputting
process sequence, process conditions, etc.

Example 1

[0076] Polishing of an edge portion of a substrate was carried out using
the polishing apparatus shown in FIG. 2. A tape having #4000 diamond
abrasive particles fixed thereon was used as a polishing tape, and a
resin pad whose lower end, which is to make contact with the polishing
tape, has a radius of curvature of 0.5 mm was used as the pressing pad of
the polishing head. While allowing the polishing tape to travel at a
speed of 10 mm/min, the polishing tape was pressed against a polishing
start position in the edge portion of the substrate, rotating at 500 rpm,
at a load of 10 N by the pressing pad of the polishing head whose
position was fixed, thereby polishing the edge portion at the polishing
start position for 20 seconds. Thereafter, polishing was continued by
pressing the polishing tape against the edge portion of the substrate,
rotating at 500 rpm, at a load of 10 N while moving the polishing head
toward the peripheral end of the substrate at a movement speed of 5
μm/min. The results of the polishing, i.e., the relationship between
polishing amount and radial position (measurement position) on the
substrate, are shown in FIG. 7.

[0077] In FIG. 7, the "notch" curve represents the polishing amount on a
line connecting the center and a notch of the substrate (center-notch
line); the "90°" curve represents the polishing amount on a line
corresponding to the center-notch line as it is rotated by 90 degrees
counterclockwise; the "180°" curve represents the polishing amount
on a line corresponding to the center-notch line as it is rotated by 180
degrees counterclockwise; and the "270°" curve represents the
polishing amount on a line corresponding to the center-notch line as it
is rotated by 270 degrees counterclockwise. This holds true for FIGS. 8
and 9.

Example 2

[0078] Polishing of an edge portion of the same substrate was carried out
in the same manner as in Example 1 except that the edge portion at the
polishing start position was polished for 40 seconds. The results of the
polishing, i.e., the relationship between polishing amount and radial
position (measurement position) on the substrate, are shown in FIG. 8.

Comp. Example 1

[0079] Polishing of an edge portion of the same substrate was carried out
in the same manner as in Example 1 except that polishing of the edge
portion of the substrate was started by pressing the polishing tape
against the polishing start position in the edge portion of the
substrate, rotating at 500 rpm, at a load of 10 N by the pressing pad of
the polishing head and, immediately after the start of polishing, the
polishing head was moved toward the peripheral end of the substrate at a
movement speed of 5 μm/min. The results of the polishing, i.e., the
relationship between polishing amount and radial position (measurement
position) on the substrate, are shown in FIG. 9.

[0080] As can be seen in FIGS. 7 through 9, the inclination at the
boundary between the polished surface and the non-polished surface is
steeper in Examples 1 and 2 than in Comp. Example 1. Further, the
inclination is steeper in Example 2 than in Example 1.

Example 3

[0081] First, an edge portion of a substrate was subjected to polishing
(rough polishing) with a polishing tape having #4000 diamond abrasive
particles fixed thereon. FIG. 10 shows a photomicrograph of a surface
area around the boundary between the polished surface and the
non-polished surface of the substrate after the rough polishing.
Thereafter, polishing of the edge portion of the substrate was carried
out in the same manner as in Example 1 except that the edge portion at
the polishing start position was polished for 10 seconds by using a
polishing tape having #12000 diamond abrasive particles fixed thereon and
pressing the polishing tape against the polishing start position of the
rotating substrate by the pressing pad of the polishing head whose
position was fixed. FIG. 11 shows a photomicrograph of a surface area
around the boundary between the polished surface and the non-polished
surface of the substrate after the polishing.

Example 4

[0082] Polishing of an edge portion of the same substrate was carried out
in the same manner as in Example 3 except that an edge portion at the
polishing start position was polished for 20 seconds. FIG. 12 shows a
photomicrograph of a surface area around the boundary between the
polished surface and the non-polished surface of the substrate after the
polishing.

Comp. Example 2

[0083] Polishing of an edge portion of the same substrate was carried out
in the same manner as in Example 3 except that polishing of an edge
portion of the substrate was started by pressing the polishing tape
against the polishing start position in the edge portion of the
substrate, rotating at 500 rpm, at a load of 10 N by the pressing pad of
the polishing head and, immediately after the start of polishing, the
polishing head was moved toward the peripheral end of the substrate at a
movement speed of 5 μm/min. FIG. 13 shows a photomicrograph of a
surface area around the boundary between the polished surface and the
non-polished surface of the substrate after the polishing.

[0084] As can be seen in FIGS. 11 through 13, sawtooth irregularities due
to uneven polishing were formed in the vicinity of the boundary between
the polished surface and the non-polished surface of the substrate after
the polishing in Comp. Example 2, whereas no such irregularities were
formed in Examples 3 and 4. This demonstrates that the polishing method
according to the present invention can prevent the occurrence of uneven
polishing.

[0085] FIG. 14 schematically shows another polishing apparatus. This
polishing apparatus, in addition to the polishing head 2 of the
above-described embodiment for polishing an edge portion of a substrate,
further includes a bevel polishing head 50 for contact with a bevel
portion of a rotating substrate W to polish the bevel portion. The bevel
polishing head 50 is disposed lateral to the substrate W held on the
substrate stage 11 of the substrate holding section 1. The bevel
polishing head 50 includes a polishing tape 52, a pressing pad 54
disposed on a back side (opposite side from a polishing surface) of the
polishing tape 52, and a pressing mechanism 56, e.g., comprised of a
cylinder, for applying a pressure to the pressing pad 54.

[0086] In operation, while supplying a polishing liquid from the polishing
liquid supply nozzle 40 onto a surface of a substrate W, which is held on
the substrate stage 11 and is rotating at a predetermined rotational
speed, the polishing tape 10 of the polishing head 2 is pressed against
the edge portion of the substrate W at a predetermined pressure and the
polishing tape 52 of the bevel polishing head 50 is pressed against the
bevel portion of the substrate W at a predetermined pressure to
simultaneously polish the edge portion and the bevel portion of the
substrate W. This embodiment can thus increase the throughput and, in
addition, can reduce the usage of a polishing liquid, thereby reducing
the production cost.

[0087] When there is a difference between the time it takes to polish the
bevel portion of the substrate W and the time it takes to polish the edge
portion of the substrate W, the polishing rate can be lowered for the
polishing head for the less time requiring polishing. Thus, the traveling
speed of the polishing tape can be slowed down, or the usage of the
polishing tape can be reduced. This can reduce the polishing cost.

[0088] Further, the overall polishing time can be shortened. This can
reduce the risk of contamination of a substrate surface in which devices
are formed.

[0089] Further, when there is an imbalance in processing time between
polishing and other processing, the processing times can be balanced by
simultaneously carrying out polishing of an edge portion of a substrate
and polishing of a bevel portion of the substrate. It thus becomes
possible to operate the apparatus in the most efficient manner.

[0090] While the present invention has been described with reference to
preferred embodiments, it is understood that the present invention is not
limited to the embodiments described above, but is capable of various
changes and modifications within the scope of the inventive concept as
expressed herein.